There is conventionally used a gas sensor for detecting the concentration of a specific component (e.g. oxygen) in an exhaust gas of an internal combustion engine. This gas sensor includes therein a gas sensor element equipped with at least one cell, each cell having a solid electrolyte body of oxygen-ion-conducting partially stabilized zirconia etc. and a pair of electrodes arranged on the solid electrolyte body. There is also known a gas sensor (such as wide range oxygen sensor, NOx sensor etc.) of the type having two or more cells, one of which is configured as an oxygen pumping cell.
It is common practice to use, as the electrodes of the oxygen pumping cell, porous electrodes each formed with a plurality of pores by adding a vanishable solid material (such as theobromine or carbon) into an electrode paste of noble metal particles and ceramic particles and then sintering the resulting paste (see Patent Document 1). The use of such porous electrodes leads to increase in the three-phase interface between the electrodes, the solid electrolyte body and the air (gas under measurement) for improvement of oxygen pumping performance.
For reduction of power consumption, the gas sensor using the solid electrolyte body is required to have low-temperature activity. In the gas sensor having the oxygen pumping cell, it is particularly required to increase the amount of three-phase interface of the electrodes of the oxygen pumping cell, allow reduction of electrode resistance and improvement of oxygen pumping performance and thereby achieve improved low-temperature activity.